Air inlet screen



May 16, 1967 w. J. RITCHIE AIR INLET SCREEN 2 Sheets-Sheet 1 Filed Dec.14, 1964 INVENTOR Wallace .lumes RITCHIE ATTORNEY y 1967 w. J. RITCHIE3,319,402

AIR INLET SCREEN Filed Dec.

2 SheetsSheet 2 INVENTOR Wallace .lumes RITCHIE ATTORNEY United StatesPatent Ofliice 3,319,402 Patented May 16, 1967 3,319,402 AIR INLETSCREEN Wallace James Ritchie, Greenfield Park, Quebec, Canada,

assignor to United Aircraft of Canada Limited, Longueuil, Quebec, CanadaFiled Dec. 14, 1964, Ser. No. 418,158 8 Claims. (Cl. 55306) The presentinvention relates to improvements in the construction of protectivescreens and more particularly to an improved construction of an airinlet screen masking the air inlet passage of a gas turbine engine.

As is Well known, it is necessary to provide a screen, protective baflleor other similar protective device in the air inlet of a gas turbineengine in order to prevent entry of any foreign matter which coulddamage the engine while it is in operation. Such a screen must be ofrigid yet flexible construction to withstand both the impact of anyforeign objects which under the influence of the intake air may strikethe screen at high velocity and also the vibrational effects of theengine in operation. The mesh or air admitting openings of the screenmust also be selected to be large enough to avoid creating an excessivepressure drop which would effect the operation of the engine and at thesame time the openings must be kept small enough to block anyappreciable sized foreign object.

With these factors in mind, the present invention aims to provide animproved air inlet screen construction which is designed particularlyfor use in a turbo-prop engine having a circular plenum chamber formedby an air inlet case. Accordingly in the preferred construction the airinlet screen is of a cylindrical form and is designed so that it can bemade in segments or as a complete cylinder.

In order to provide the desired structural rigidity and to avoidsupplementary reinforcing members which would add additional weight, thepresent screen construction is made from a sheet or sheets of perforatedsheet metal which is corrugated lengthwise to make it self-supporting.This corrugated construction permits flexibility in the manner ofassembly while providing excellent impact resistance. In addition,increased structural integrity may be obtained by introducing solidboundaries at specified locations.

The diameter of the perforations in the sheet are selected to providemaximum air flow while preventing passage of any foreign particles of adimension liable to cause damage to the engine. As will be appreciatedthe nature and extent of both corrugations and perforations may bevaried dependent on application and environment. There is anotheradvantage in the present construction in that intake noise suppressionis added by the defraction of sound waves due to the perforations andsome noise scattering caused by the convolutions of the screen material.

Specifically, the screen sections are provided with integral outwardlyextending flanges along their free edges and these are overlapped bysupplementary flange sections so that the necessary joint or joints aremade by butting the adjacent flanges together with a rubber gaskettherebetween. The ends of the resultant cylindrical screen are providedwith overlapping annular gaskets, preferably of rubber, which provide aseal about the engine air intake when the screen is installed and alsoprovide additional vibration damping as well as allowing for moretolerance in manufacturing and assembly of screen elements. A feature ofthe present construction resides in the provision of one or morelocating dowel-pins which extend outwardly from one or both of the endsof the air inlet screen and engage with corresponding openings providedin the air inlet casing to ensure proper alignment and prevention ofrotation.

Having thus generally described the nature of the invention, particularreference will be made to the ac companying drawings showing a preferredembodiment thereof, and in which;

FIGURE 1 is a side view of the air inlet screen according to theinvention as it would appear in operative position surrounding acircular plenum chamber formed by the air inlet core of an in-line freeturbine engine.

FIGURE 2 is a sectional view of FIGURE 1 along the line 2-2 showing theconstruction and assembly of the top interconnecting flanges of thescreen sections.

FIGURE 3 is a sectional view of FIGURE 1 along the line 33 showing theconstruction and assembly of the lower interconnecting flanges of thescreen sections.

FIGURE 4 is a sectional view, broken for convenience, of theconstruction of FIGURE 1 along the line 44 to show in more detail theattachment of the locating dowelpin and construction and attachment ofthe end gasket flanges.

FIGURE 5 is an enlarged detail view of a section of one end of a screensection to illustrate a preferred perforation pattern and means ofattachment of the gasket flange.

FIGURE 6 is a sectional view of FIGURE 5 along the line 66 to show thepreferred relationship of corrugations and perforations and gasketflange.

With particular reference to FIGURES 1 and 2 of the drawings an airinlet screen assembly 10 according to the invention is shown inoperative position surrounding a circular air plenum .formed in an airinlet case A of an in-line gas turbine engine.

The air inlet screen assembly 10 as shown is made up of two equalsections 12, 12a of perforated met-a1 sheet which are corrugatedlongitudinally as indicated at 14 and formed to the desiredsemi-circular contour to form the main body of the cylindrical screenassembly 10. It will be appreciated that the present screen constructioncan be made in two segments as shown, more than two segments, or as asingle cylindrical section, depending on requirements and conditions ofassembly, without departing from the design of the invention.

In the construction illustrated, and this will be typical of alternativeconstructions, the free longitudinal 3 edges of each perforatedcorrugated section 12, 12a is bent upwards to form an integral flange 16and this flange 16 is overlapped and reinforced by an angularreinforcing flange 18. In the preferred construction the flange 18 isplaced over the integral flange 16 and the two joined together forexample, by spotwelding.

In order to obtain a close seal between the screen sections and to aidin the general flexibility of the structure with respect to assembly,each flange 18 is provided with a sealing strip 20, of rubber or thelike, which is secured to the flange 18 by suitable means. The flanges18 of the respective sections are connected in face to face relationshipon assembly by suitable bolts and nuts 22 as shown. To provideadditional flexibility on assembly and to provide a seal between theends of the present air inlet screen and the engine air inlet case A,each screen section 12, 12a is provided along the opposing transaxialends with a flexible gasket strip 24, as shown in FIGURE 4. Thesegaskets 24 are preferably made of rubber with an internal slot or groove26 which accommodates the thickness of the perforated screen plate andthey are attached to the plate edges by heat and pressure or a suitableadhesive so that they are firmly bonded in place. As will be understoodby reference to the preceding desc-ription and the accompanyingdrawings, each air inlet screen section is a complete unit, which can be3 readily replaced in the event of damage, having connecting flanges 18with sealing strips 20 and flexible gaskets 24 attached to the mainscreen body at each end.

In order to provide a ready means for locating the screen sectionsrelative to an air inlet case, for example the case A in theconstruction shown, each section is provided with a locating dowel-pin28 as shown most clearly in FIGURE 4. Each locating pin 28 is. made upof a main pin portion 28a which fits within a locating opening in theair inlet casing A and a reduced shank portion 28b which passes throughthe perforated plate 12 and associated sealing gasket 24, and through awasher 30 over which it is headed as indicated at 31. These locatingdowel-pins 23 also insure that the air inlet screen assembly ispositioned properly axially and longitudinally with respect to theengine casing and further prevents rotation of the screen assemblyduring operation.

In the preferred air inlet screen shown the perforated metal sheetutilized was stainless steel with .043".O45" diameter holes at a.058.062" diagonal pitch the corrugations being formed later. Thespacing between centers of the corrugations is about .200".225" withabout .040"-.O60" radius using .025" gauge material. This was for ascreen having about a 16 diameter and an effective axial length of about8".

I claim:

1. A self-supporting air inlet screen adapted for attachment about a gasturbine engine air inlet plenum of circular outline, said inlet screencomprising, at least one rectangular section of perforated metal sheetcorrugated longitudinally and shaped to conform to circular outline asdefined by said engine plenum, interconnecting means on the opposedmarginal edges of each of said formed sections in substantial parallelalignment with said sheet corrugations, and flexible sealing means ateach end of said formed section disposed transversely of said sheetcorrugations, and locating means on each of said corrugated formedsections whereby each section may be positively located longitudinallyrelative to said engine air inlet plenum.

2. A self-supporting air inlet screen as claimed in claim 1 wherein saidformed section interconnecting means includes outwardly extendingintegral flanges on each of said opposed marginal edges and acorresponding supplementary stiffening flange combined with andconconnected to each of said integral flanges, a flexible sealing stripmounted on the inner face of each of said supplementary flanges andfastening means passing through said combined flanges and securing oneto the other to retain said sections in said circular outline.

3. An air inlet screen as claimed in claim 1 wherein the perforations ineach section are from about .040" to about .050" in diameter.

4. An air inlet screen as claimed in claim 2 wherein each of saidsupplementary flanges consists of a strip of metal folded over on itselfand formed to an angular shape, said perforated metal section integralflange fitting between the opposed sides of said folded oversupplementary flange.

5. A self supporting air inlet screen as claimed in claim 1 wherein saidflexible sealing means each comprise a longitudinally slotted strip ofresilient material and each of said section end marginal portions arefitted within said slot and secured thereto.

6. In a gas turbine powerplant including means defining an annular airinlet passageway having bordering Walls, a self-supporting air inletscreen of cylindrical formation extending between said bordering wallsand masking said annular air inlet passage, said air inlet screen madeup of at least one fomed section of perforated metal strip corrugated atregularly spaced intervals about its circumference and in the axialdirection of said cylindrical screen, means for sealing the connectionbetween said bordering walls and screen, and locating means on saidscreen whereby it is located relative to said air inlet passageway inthe longitudinal and circumferential directions and also to preventrotational movement of said screen relative to said passageway borderingwalls.

7. In a gas turbine powerplant as claimed in claim 6 wherein saidcylindrical air inlet screen is made up of two equal sectionsinterconnected at diametrically opposed points.

8. In a gas turbine powerplant as claimed in claim 6 wherein saidlocating means comprise at least one 10- cating pin extending from aninner surface of said screen adapted to overlap said passagewaybordering walls.

References Cited by the Examiner UNITED STATES PATENTS 1,854,160 4/1932Baird -529 X 2,928,497 3/1960 Stockdale 55306 FOREIGN PATENTS 471,5609/1937 Great Britain. 694,578 7/1953 Great Britain.

HARRY B. THORNTON, Primary Examiner.

S. W. SOKOLOFF, Examiner.

1. A SELF-SUPPORTING AIR INLET SCREEN ADAPTED FOR ATTACHMENT ABOUT A GASTURBINE ENGINE AIR INLET PLENUM OF CIRCULAR OUTLINE, SAID INLET SCREENCOMPRISING, AT LEAST ONE RECTANGULAR SECTION OF PERFORATED METAL SHEETCORRUGATED LONGITUDINALLY AND SHAPED TO CONFORM TO CIRCULAR OUTLINE ASDEFINED BY SAID ENGINE PLENUM, INTERCONNECTING MEANS ON THE OPPOSEDMARGINAL EDGES OF EACH OF SAID FORMED SECTIONS IN SUBSTANTIAL PARALLELALIGNMENT WITH SAID SHEET CORRUGATIONS, AND FLEXIBLE SEALING MEANS ATEACH END OF SAID FORMED SECTION DISPOSED TRANSVESELY OF SAID SHEETCORRUGATIONS, AND LOCATING MEANS ON EACH OF SAID CORRUGATED FORMEDSECTIONS WHEREBY EACH SECTION MAY BE POSITIVELY LOCATED LONGITUDINALLYRELATIVE TO SAID ENGINE AIR INLET PLENUM.